Pins landing on visible cosmetic faces
- Circular witness and slight gloss difference around the push point
- Texture can hide minor witness but not a deep pin crush
- Repositioning pins later requires welding and re machining steel
Glossary
What Is an Ejector Pin? Injection Molding Explained
Ejector pins are the push points that release the part from the core after the mold opens.
Glossary
Ejector pins push the cooled part off the core after the mold opens
Pin witness marks are a cosmetic and DFM topic, not only a maintenance item.
After pack and cooling, plastic shrinks onto core details. Ejector pins apply force on planned push points so the part releases without bending thin walls or tearing ribs.
Pin location, diameter, and stroke must match draft, texture, and undercut strategy. Moving pins after steel is cut is expensive compared with marking push faces in CAD early.
Production tools use hardened steel pins sized for repeat cycles. Prototype shortcuts that leave parts stuck are a signal that ejection was under planned.
Glossary
How ejector pin shows up on real programs
Library photos illustrate molding and tooling context for this term.
- Use the term in RFQs with geometry and material context, not in isolation.
- Link to the design guide when the term affects steel or part design.
- Upload CAD when the term changes tooling scope or piece price.
Cosmetics
Pins on hidden faces versus Class A surfaces
Every pin leaves a witness. The question is whether your drawing accepts it.
Pins on functional or hidden faces
- Witness acceptable when called out on the drawing
- Multiple smaller pins spread load on thin walled parts
- Stripper plates can reduce direct pin contact on large flat cores
RFQ
Ejection notes mold designers use from your CAD
These reduce T1 surprises when parts stick or show pin blush.
Faces that cannot accept ejector witness marks
Deep cores or tall ribs that need balanced push points
Soft elastomer or TPE parts that tear if pins are too small
Robot grip plan if parts must leave the mold without manual pry
Go deeper
Where this term connects
Each link is a different angle on the same program, not a duplicate definition.
Core
Most ejection loads start from core side geometry.
CoreDesign guide hub
Draft and wall rules before pins touch the part.
Design guide hubA side and B side
Ejection usually lives on the moving half.
A side and B sideDesign guide hub
Wall, rib, and draft rules tied to ejection.
Design guide hubVisual reference
Photos from molding and tooling programs
Images are selected from the NetProto Forge media library for this topic.
Injection molded production parts on a tray
Injection molded production parts on a tray
Engineer reviewing a molded part drawing
Engineer reviewing a molded part drawing
Plastic housing components from a steel tool
Plastic housing components from a steel tool
FAQ
Ejector pin questions
Can ejector pins be eliminated?
Some parts release on draft alone. Most production geometries need planned push points.
Why do parts stick even with pins?
Insufficient draft, vacuum in deep cores, or soft material tearing at pin edges are common causes.
Do pin marks affect paint or pad print?
Raised or rough witness can telegraph through coatings. Call out cosmetic zones early.
Next step
Plan ejection in DFM
Upload CAD with cosmetic faces and deep cores marked before approving steel.